M. Visscher et Kg. Struik, OPTICAL PROFILOMETRY AND ITS APPLICATION TO MECHANICALLY INACCESSIBLESURFACES .1. PRINCIPLES OF FOCUS ERROR-DETECTION, Precision engineering, 16(3), 1994, pp. 192-198
Optical profilometers can in principle be used to measure the roughnes
s of surfaces that are not accessible for mechanical profilometers. Op
tical measurements can be performed through a transparent layer becaus
e of the noncontacting nature of the measuring principle. In this arti
cle the properties of a focus error detection system are given for the
general case of scanning free surfaces and for the particular case of
a glass plate lying on the scanned surface. Tests show that scanning
through a glass plate is possible, but there are some limitations. The
conditions under which proper measurements can be performed are descr
ibed. Some examples of scanning through a transparent layer will be pr
esented in part II of this paper.